The universe is ruled by entities known variously as the Great Old Ones, Old Ones, Ancient Ones, Outer Gods, Elder Gods, Other Gods, and similar terms. All the races and beings of the Mythos are aware of these entities—some view them as equals, some treat them as enemies, and some even worship them. Many have cults among humanity or other races, which serve these beings in hopes of terrible returns.

The different titles by which these eldritch beings are known usually represent different types or orders of power. For example, the Outer Gods or Other Gods are of cosmic interdimensional import. Many of them are blind and idiotic, though this does not diminish their power. The Outer Gods are linked together in some way unknowable to mortals, and their chief is the Daemon Sultan Azathoth. When certain events transpire in our universe, the Outer Gods are disturbed, and they send Nyarlathotep or another envoy to inspect the disturbance.

The entities known as Great Old Ones appear to be enormous and influential alien beings, rather than cosmic principles. Each Great Old One is autonomous: they are not connected like the Outer Gods, and they sometimes view each other with hostility. All Great Old Ones violate the natural laws of the universe, and have achieved their supreme power in different ways. The famed being known as Cthulhu is itself a Great Old One.

There exist numerous and complex tiers of entities of various sorts, as noted below in the various descriptions of these beings. What unites them all is the great danger they pose not only to adventurers, kingdoms, and the world, but to all the multiverse.

When an unfortunate party of adventurers runs into one of these terrible beings, the result is nothing like a typical battle or conventional encounter. Natural laws ripple and flow. The entity itself violates previously-solid states of matter and mind. The whole world goes mad, at least locally. In essence, the Great Old Ones (or Other Gods, or Elder Gods, etc.) act as an environmental effect. Typically, adventurers can hope only to escape the effect somehow, and rarely do they achieve a victory greater than survival.

The important thing to remember is that Great Old Ones and their kind do not act as if they are monsters. They don’t have hit points or armor classes or attacks in the normal sense, though their powers may mimic some of these characteristics. For example, in many cases, inflicting damage will not harm a Great Old One but can help dispel a Great Old One’s local presence.

Reading an Elder Influence Stat Block

Each of the powerful entities presented in the following pages are summarized in the same way—with an “Elder Influence stat block.” These stats do not present the entities as monsters per se (although in many cases, certain aspects of an Elder Influence utilize monsters as effects), but are more akin to hostile environments.

An Elder Influence can manifest in the world in any number of ways—perhaps as the result of a powerful ritual performed by a group of insane cultists, or maybe simply because the adventurers couldn’t resist opening a forbidden locked door beyond which the Elder Influence was housed.

Note that the advent of Elder Influences should be significant events in your campaign, preferably the climax of a long series of events or adventures. The methods by which an Elder Influence can be established in your world are left deliberately nebulous, so that individual GMs can allow them to manifest in whatever way makes sense for their campaigns.

Perhaps a group of dedicated cultists have uncovered a secret ritual and if the PCs don’t defeat the cabal in time, they manage to establish an Elder Influence to their god. Or maybe that group of cultists has already established an Elder Influence and the PCs must go on several quests to defeat or banish it. Perhaps the stars have just aligned, and an Elder Influence simply manifests because its time has come. Whatever the reason, defeating an Elder Influence should be a major event in a campaign, and the experience points awarded for such a defeat are significant. They are as much a reward for surviving a difficult encounter as they are a story reward for advancing the plot and, if not outright saving the world, then at least giving the world a few more years to exist before the next threat rises!

Elder Influence Name and Challenge Rating: The name of the Elder Influence is presented first, along with its challenge rating (CR) at its lowest stage of influence. If an Elder Influence has additional influence stages (see Influence Stage, below), its challenge rating increases by +3 per stage. For example, Great Cthulhu is a CR 21 Elder Influence while at influence stage 1, but increases to CR 24 at stage two, CR 27 at stage 3, and finally to CR 30 at stage 4. Defeating an Elder Influence earns experience points as appropriate for the highest CR the influence reached; it does not award extra XP for lower CRs represented by lower influence stages.

Alignment, Entity Type, and Areas of Concern: The alignment of the entity associated with the Elder Influence is listed here, along with its categorization, be it Great Old One, Old One, Ancient One, Outer God, Other God, or something else entirely. All of these entities are worshiped by cults and can grant spells, though many of them have no interest in their cults and, indeed, may not even be aware of them. The areas of concern listed here are as much the creation of their cultists as they are legitimate interests of the entity itself.

Primary Source: This line lists the original creator of the entity, as well as the first significant story in which the entity appeared. In some cases (such as Hastur), the entity is the result of multiple primary sources and authors, in which case additional entries appear as appropriate on this line.

Cult: The section of the statistics listed under “Cult” pertains to those who worship the entity. These are popular tendencies among the deity’s worshipers— individual cultists of one of these entities may vary as widely as they do.

Domains: This section lists the domains that the entity grants to its clerics. Less powerful entities (such as Great Old Ones, Old Ones, and Ancient Ones) grant four domains, while more powerful entities (such as Outer Gods or Other Gods) grant five domains.

Subdomains: This section lists the subdomains the entity grants to its clerics. Less powerful entities (such as Great Old Ones, Old Ones, and Ancient Ones) grant four subdomains, while more powerful entities (such as Outer Gods or Other Gods) grant six subdomains.

Favored Weapon: The favored weapon of the cult is listed here. Note that in many cases, the Elder Entities themselves do not utilize weapons of a manufactured nature; as such, favored weapons are largely traditional choices selected by the cult’s founders.

Symbol: This entry describes the most common symbol used by the cult to represent its eldritch patron.

Temple: This line lists typical examples of the buildings or locations that are sacred to the entity’s cult, which are used as places of worship.

Worshipers: This entry describes in general terms the sorts of worshipers who may belong to the entity’s cult. Specifications may include specific races of creature or a mindset or interest. These entries are not meant to be exhaustive, but merely point out the typical types of people who worship the entity.

Servitors: This line lists a few monsters from this book that are often associated with the entity’s cult.

Influence: This section of the stat block presents the effects of the entity’s manifestation in a region. In some cases, an entity may have multiple stages of influence to model its growing power, while in others, an entity has only a single influence stage. For each influence stage, a DC is listed in parenthesis—this is the save DC to resist or negate any of the influence’s effects.

CR and XP: At stages higher than stage one, the influence’s increased CR and XP awards are listed for ease of reference.

Speed: An influence can move at the speed listed. If an influence has a climb, fly, or swim speed, it automatically succeeds on all skill checks needed to move. If an influence has no speed listed, then it is immobile. Except as noted otherwise, an influence (or its nucleus) can't be moved by teleportation effects unless its center (or nucleus, if it has one) will arrive in a location that was already within the area of the influence (see below).

Area and Nucleus: An influence affects an area. Often, a physical manifestation of the creature appears as a nucleus for the influence that is contained wholly in the area but does not completely fill this area. When an influence has a nucleus listed, this indicates the space that this physical manifestation takes up at the center of the area. When no nucleus is listed, the area itself has no central physical manifestation. In such cases, the influence cannot typically be harmed by damage and its defeat requires other tactics. Other creatures can move through an influence’s area, but while they are within the area, they are subject to the influence’s effects. A creature cannot move through a nucleus, nor can a nucleus be moved against its will.

AC, Saves, and Hit Points: If an influence can be harmed by damage, its Armor Class, saving throws, and hit points are listed here. (See “Running an Encounter with an Elder Influence” below for more information.) This line is omitted if the influence cannot be harmed by damage—in such cases, other steps must be taken to defeat the influence.

Effects: All influences have effects that target and affect all within their areas. Full details for these effects are given at the end of the stat block.

Proxy: Some influences have a proxy—a single creature that is tied to the influence and serves as its nucleus. A proxy cannot leave the area of an influence, but otherwise functions as normal for a monster. Some influences use a standard monster presented elsewhere in this book as a proxy, while others are themselves the proxy. A proxy is never harmed or hindered by the effects of its own influence. Typically, an influence with a proxy can be ended by slaying or defeating the proxy creature. This line is omitted if the influence has no proxy. (Note that in some cases, an influence might have a proxy at one stage but not another, so this line might be omitted for one stage and appear under another.)

Escalation: If an influence has multiple stages, the conditions that must be met for it to advance to a higher stage are listed here. For an influence with only one stage, or for an influence’s maximum stage, this line is omitted.

Defeat: Fortunately for humanity, all influences can be defeated by certain conditions or actions. Unfortunately for humanity, these conditions and actions are typically very complex or dangerous undertakings. Worse, fulfilling them does not permanently defeat the entity itself, whose influence can manifest again and again as the conditions allow.

At best, adventurers can achieve fleeting victories against the influence, preserving the world for a time before the next, inevitable incursion. This section only lists the most typical and common method of defeating the influence—typically, by combating the influence directly or by defeating its proxy. In some cases, other, more obscure and complex methods for defeating an influence may exist, often requiring long and dangerous rituals or quests to complete. This is left to the GM’s discretion.

Influence Effects: Finally, any of the influence’s effects are detailed in full here.

Running an Encounter with an Elder Influence

For the most part, influences function more like environmental effects than monsters. For most influences, inflicting damage can be a method (if desperate) of driving the entity off, at least temporarily. Initiative: An Elder Influence always goes first in a combat round, moving its speed if it wishes to position itself in a more advantageous location.

Resistances and Immunities: If an influence can be damaged, attacks (be they melee or ranged, magical or mundane) must be directed at the influence’s nucleus at the center of its area. An influence is immune to all spells and effects that don’t inflict raw hit point damage (including effects that arbitrarily reduce a target to a set number of hit points, such as phantasmal killer), unless otherwise specified in the specific influence’s stats.

Armor Class: Attacks against an influence always resolve against a fixed AC, regardless of whether the attack is a touch attack or a flat-footed attack.

Saving Throws: When an attack allows a saving throw to reduce or negate the damage the attack inflicts, an Elder Influence uses a static modifier for its save as listed in its stats, regardless of whether the effect calls for a Fortitude, Reflex, or Will saving throw.

Hit Points: An Elder Influence takes half damage from all sources. Due to its lack of discernible anatomy, an Elder Influence does not suffer additional damage from critical hits, nor from precision-based damage, such as that from a rogue’s sneak attack. In certain cases, specific forms of damage might have no effect or might have an augmented effect on an Elder Influence (such as inflicting normal damage), as noted in its statistics.

The monstrosity hangs in the air: a rapidly-growing mass of pseudopods, cosmic force, and fields of energy. Overall it resembles a terrestrial star, with a central eye that opens into an eternity of madness.

This colossal, corpulent dragon-octopus hybrid possesses bat-like wings, huge talons, and a face that is a mass of tentacles and feelers. Green and ever-shifting, its carapace ranges from gelatinous to chitinous.

This terrifying entity is large and horribly unlike anything else of a normal evolutionary background. It rears up, its underside bristling with eye-like, otherworldly globes and portals swirling with colors.

A huge worm-like mass thrusts up from the world’s crust, then blossoms into a unique, impossible form. A bright white light shines from its tip as it throbs in time with the unceasing wrenching of the earth.

A three-legged, headless monster howls at you from the gloom. The top of its body ends in a single tapering tentacle, which quivers and waves at the sky. Visibly in its transparent gut, it digests wraith-like souls, and a glowing organ shines from the center of its body. It has two clawed hands that wave in arcane patterns.

This terror takes the form of a withered and mummified human fetus. Its bones are ankylosed together, and its arms stretch rigidly forward. It appears in a pillar of moonlight and descends slowly toward its target, seemingly unable to move its limbs, eternally fixed in its tormented pose.

This interstellar being has a rounded torso and long sinuous limbs ending in crab-like claws. Its head protrudes from one side, ending in a flexible proboscis, marked with three eyes and a row of gill-like lateral lines along its neck.

This fungus-like organism uses huge arcane tablets of stone to give its body structure. It has both tentacles and fruiting bodies and is topped with a lumpy mass that oozes a cloud of foul-smelling spores.

A monstrous, serpent-tailed being with foreclaws and an armored hide, creature possesses a medusa-like thicket of snakes sprouting from its forebody where its head should be. A massive serpentine trunk ending in an enormous eye extends above the thicket, waving ominously.